The orthodontic appliance is fitted by bonding its bracket to the tongue side face of a tooth of a patient. Since the tongue side face of the tooth has a more complicated shape than that of a lip side face, it is difficult to bond the bracket to an ideal position.
In order to bond the bracket to the ideal position on the tongue side face of the tooth, there has been adopted an indirect bonding method using the T.A.R.G. (Torque Angulation Reference Guide) or the C.L.A.S.S. (Custom Lingual Appliance Setup System). When the bracket is to be bonded to the tooth of the patient, according to that method, three to six teeth are individually bonded by using a bracket fitting core (or indirect tray) made of a flexible member such as silicone.
In the C.L.A.S.S., on the other hand, there is used a set-up tooth impression in which the tooth impression of the patient is re-arrayed into a target state, so that the bracket can be positioned more correctly than the T.A.R.G. This set-up tooth impression is prepared by forming a duplicate mold from the original impression mold of the tooth impression of the patient and by dividing the duplicate mold into individual teeth to re-array them.
In order to form the indirect tray by using the set-up tooth impression, the bracket is positioned at first with respect to the set-up tooth impression by using a gauge or the like, and the gap between the positioned bracket and the mold is filled with an adhesive (or an advance adhesive). As a result, the base face of the bracket is formed to conform to the tongue side face intrinsic to each tooth (advance of bracket). Next, the bracket positioned with respect to the set-up tooth impression is returned to the original impression mold, and the indirect tray is formed by covering the original impression mold with the silicone.
The indirect tray over all the teeth is usually divided into those for three to six teeth. Then, the adhesive is applied to the base face of the advanced bracket, and the indirect tray is fitted to the teeth of the patient, so that the bracket is bonded to the teeth of the patient. Finally, the indirect tray is removed from the bracket.
However, the indirect tray of the prior art has the following problems.
First of all, in both the T.A.R.G. and the C.L.A.S.S., the indirect tray extends over the three to six teeth and has flexibility so that it is liable to distort. This may cause a displacement of the bracket when this bracket is fitted to the teeth of the patient.
At the fitting time, on the other hand, the tray may distort to float the base of the bracket from the teeth of the patient. This makes it necessary to apply more adhesive to ensure the adhesion and fitting. If much adhesive is applied to the bracket, however, the excess adhesive will exude from the fitting face. This makes a work necessary for removing the excess adhesive.
Since the indirect tray of the prior art has a size to extend over the three to six teeth, moreover, it has to be supported till the adhesive sets after it was fitted to the teeth of the patient, so that it may go out of position.
Since the indirect tray of the prior art samples not only the tooth shape of the patient but also the alignment of teeth, still moreover, it cannot be used if the tooth alignment of the patient changes after the sampling of the tooth impression of the patient and before the fitting of the bracket. For this time period, therefore, it is impossible to extract or separate the tooth.
Next, according to the method using the C.L.A.S.S., the bracket has to be returned to the original impression mold after it was advanced with the set-up tooth impression. Since the original impression mold has to be left as it is, therefore, a duplicate is required for forming the set-up to the impression.
In order to return the bracket to the original impression mold, on the other hand, complicated technical works are required for making a person tray or for forming a notch or mark in the original impression mold. With these troubles, the bracket may goes out of position when it is returned to the original impression mold.